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Behav Pharmacol. 2013 Sep;24(5-6):504-16. doi: 10.1097/FBP.0b013e328363d1c4.

Comparison of a drug versus money and drug versus drug self-administration choice procedure with oxycodone and morphine in opioid addicts.

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Department of Psychiatry, Division on Substance Abuse, New York State Psychiatric Institute, College of Physicians and Surgeons of Columbia University, 1051 Riverside Drive, Unit 120, New York, NY 10032, USA.


This double-blind, placebo-controlled study investigated the effects of oral morphine (0, 45, 135 mg/70 kg) and oral oxycodone (0, 15, 45 mg/70 kg) on buprenorphine-maintained opioid addicts. As a 3: 1 morphine : oxycodone oral dose ratio yielded equivalent subjective and physiological effects in nondependent individuals, this ratio was used in the present study. Two self-administration laboratory procedures - that is, a drug versus money and a drug versus drug procedure - were assessed. Study participants (N=12) lived in the hospital and were maintained on 4 mg/day sublingual buprenorphine. When participants chose between drug and money, money was preferred over all drug doses; only high-dose oxycodone was self-administered more than placebo. When participants chose between drug and drug, both drugs were chosen more than placebo, high doses of each drug were chosen over low doses, and high-dose oxycodone was preferred over high-dose morphine. The subjective, performance-impairing, and miotic effects of high-dose oxycodone were generally greater than those of high-dose morphine. The study demonstrated that a 3: 1 oral dose ratio of morphine : oxycodone was not equipotent in buprenorphine-dependent individuals. Both self-administration procedures were effective for assessing the relative reinforcing effects of drugs; preference for one procedure should be driven by the specific research question of interest.

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